In loading and unloading cargo packed in individual, discrete units from the hold of a ship, it is common practice to mount a vertically extending conveyor on a loading dock. A conventional cargo transport system also includes a lateral conveyor upon the deck of a vessel which directs movement of discrete cargo loads along a path terminating at a loading station on the vessel. The cargo loads may then be transferred to the vertically extending conveyor. The vertical conveyor tower includes an endless conveyor means formed with discrete receptacles traversing the length of the tower, so that each of the receptacles sequentially approaches the loading station to receive a cargo load.
The prior art systems have heretofor involved certain problems however. For example, in the aforementioned United States patent application, the powered lateral conveyor system includes a powered conveyor means at the loading station. Load checking means are provided in that system to prevent additional loads from approaching the transfer mechanism and from approaching the loading station when the transfer mechanism is actuated and unable to accept additional loads. While this feature was designed to prevent cargo boxes from piling up at the transfer mechanism, a problem results because after transfer of a load to the vertical conveyor system, the inertia of the following boxes must be overcome for loading of the subsequent boxes to proceed. By providing a powered conveyor means at the loading station with a checking means to prevent the advance of cargo loads during the periods of time when the transfer mechanism is unavailable to accept such loads, an irregular, jerking motion is introduced into the train of cargo loads being transferred to the vertical conveyor system. Because of this "inch-worm" effect, advancement of cargo loads for off loading is held up by the load checking devices in the conventional lateral conveyor systems. Thus, the time required to unload a vessel is increased.